Boiling, Evaporating, and Condensing | 沸腾、蒸发与凝结

📚 Boiling, Evaporating, and Condensing | 沸腾、蒸发与凝结

Boiling, evaporating, and condensing are three important changes of state. They explain how water turns into steam, how puddles dry up, and how clouds form. In KS3 chemistry, you need to use the particle model to describe these processes and to compare boiling with evaporation.

沸腾、蒸发和凝结是三种重要的物态变化。它们解释了水如何变成蒸汽、水坑如何变干以及云如何形成。在 KS3 化学中，你需要用粒子模型来描述这些过程，并比较沸腾与蒸发。

1. States of Matter and the Particle Model | 物质状态与粒子模型

All substances are made of tiny particles. In a solid, particles are packed closely in a fixed arrangement and can only vibrate. In a liquid, particles are still close but can move around each other. In a gas, particles are far apart and move quickly in all directions.

所有物质都由微小粒子组成。在固体中，粒子紧密排列在固定位置上，只能振动。在液体中，粒子仍然靠得很近，但可以相互滑动。在气体中，粒子相距很远，并朝各个方向快速运动。

Boiling and evaporation both change a liquid into a gas. Condensing is the reverse change: a gas becomes a liquid. These processes can be explained by how much energy the particles have.

沸腾和蒸发都是把液体变成气体。凝结则是相反的变化：气体变成液体。这些过程可以用粒子所具有的能量多少来解释。

2. What Is Boiling? | 什么是沸腾？

Boiling is the change of state from liquid to gas that happens throughout the whole liquid. When a liquid is heated strongly, bubbles of gas form inside the liquid and rise to the surface.

沸腾是液体整体从液态转变为气态的过程。当液体被强烈加热时，液体内会形成气泡并上升到表面。

The bubbles in boiling water are not air. They are bubbles of water vapour, which is water in the gas state. The temperature at which a liquid boils is called its boiling point.

沸腾水中的气泡不是空气。它们是水蒸气气泡，也就是气态的水。液体沸腾时的温度称为沸点。

At standard atmospheric pressure, pure water boils at 100 °C. Different substances have different boiling points. For example, ethanol boils at about 78 °C.

在标准大气压下，纯水在100 °C时沸腾。不同物质有不同的沸点。例如，乙醇约在78 °C时沸腾。

3. Boiling Point and Pressure | 沸点与压强

The boiling point of a liquid is not always the same. It depends on the pressure pushing down on the liquid surface. At higher pressure, particles need more energy to escape, so the boiling point is higher. At lower pressure, the boiling point is lower.

液体的沸点并不总是相同。它取决于作用在液体表面上的压强。压强较高时，粒子需要更多能量才能逸出，因此沸点较高。压强较低时，沸点较低。

This is why water boils at a lower temperature on a high mountain. At the top of Mount Everest, the air pressure is much lower, so water can boil at around 70 °C instead of 100 °C.

这就是为什么水在高山上会在较低温度沸腾。在珠穆朗玛峰顶，气压低得多，因此水大约在70 °C就能沸腾，而不是100 °C。

A pure substance has a sharp, fixed boiling point. A mixture often boils over a range of temperatures because it contains different substances.

纯物质有清晰、固定的沸点。混合物往往在一个温度范围内沸腾，因为它含有不同物质。

4. What Is Evaporating? | 什么是蒸发？

Evaporating is the change from liquid to gas that happens only at the surface of a liquid. It can occur at any temperature below the boiling point. In evaporation, only the fastest particles at the surface have enough energy to escape into the air.

蒸发是仅在液体表面发生的由液态到气态的变化。它可以在低于沸点的任何温度下发生。在蒸发中，只有表面运动最快的粒子有足够能量逸出到空气中。

When the fastest particles leave a liquid, the average energy of the remaining particles decreases. This is why evaporation cools a liquid down. It is also why sweating cools your skin.

当最快的粒子离开液体时，剩余粒子的平均能量降低。这就是蒸发会使液体冷却的原因。这也是出汗能使皮肤降温的原因。

5. Boiling vs Evaporation: Key Differences | 沸腾与蒸发的关键区别

Boiling and evaporation both turn a liquid into a gas, but they are not the same. Boiling happens throughout the liquid at the boiling point. Evaporation happens only at the surface and can happen at any temperature.

沸腾和蒸发都能把液体变成气体，但它们并不相同。沸腾在沸点时发生在整个液体中。蒸发只发生在表面，并且可以在任何温度下发生。

The table below compares the two processes.

下表比较了这两种过程。